Modified IGF1 polypeptides with increased stability and potency

ABSTRACT

A targeting fusion protein comprising a component that comprises a (i) ligand or derivative or fragment thereof that binds a pre-selected target surface protein, such as a receptor, and (ii) an active agent or therapeutic agent(s), and further optionally (iii) a multimerizing component and/or (iv) a signal sequence. In a preferred embodiment, the targeting fusion polypeptide targets muscle and is useful to treat a muscle-related disease or condition, such as muscle atrophy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC § 119(e) of U.S. Provisionals 60/507,168 filed 30 Sep. 2003, 60/516,806 filed 3 Nov. 2003, 60/573,525 filed 21 May 2004, 60/534,819 filed 7 Jan. 2004, 60/584,956 filed 2 Jul. 2004, 60/529,826 filed 16 Dec. 2003, 60/534,654 filed 7 Jan. 2004, 60/581,833 filed 22 Jun. 2004, and 60/554,640 filed 19 Mar. 2004, which applications are herein specifically incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to therapeutic fusion proteins, methods of producing such fusion proteins, and methods for treating, diagnosing, or monitoring diseases or conditions using these proteins.

BRIEF SUMMARY OF THE INVENTION

In the broadest embodiment, the present invention comprises compositions and methods for delivering one or more active or therapeutic agent(s). In one embodiment, the present invention provides compositions and methods for specifically delivering one or more active or therapeutic agent(s) to a pre-selected target site. In this embodiment, the present invention provides fusion polypeptides capable of delivering one or more active or therapeutic agent(s) to a target site defined by the presence of one or more expressed cell surface proteins. The targeting fusion polypeptides are therapeutically useful, as well as useful in a variety of in vitro and in vivo diagnostic and prognostic assays.

In a first aspect, the invention provides a targeting fusion polypeptide comprising (i) a targeting ligand, or derivative or fragment thereof, capable of binding specifically to a pre-selected cell surface protein, and (ii) an active or therapeutic agent. In specific embodiments, the targeting fusion polypeptide optionally further comprises (iii) a multimerizing component capable of forming a multimer with another targeting fusion polypeptide, and/or (iv) a signal sequence.

In a second aspect, the invention provides a muscle-targeting fusion polypeptide, comprising (i) a targeting ligand, or derivative or fragment thereof, capable of binding specifically to a muscle cell surface protein, and (ii) an active or therapeutic agent. In specific embodiments, the muscle-targeting fusion polypeptide optionally further comprises (iii) a multimerizing component capable of forming a multimer with another targeting fusion polypeptide, and/or (iv) a signal sequence.

In specific embodiments, the muscle-targeting ligand specifically binds a muscle surface protein, such as a receptor. In a more specific embodiment, the muscle surface receptor is MuSK. In an even more specific embodiment, the muscle-targeting fusion polypeptide specifically targets skeletal muscle, and comprises a MuSK ligand, or fragment of a MuSK ligand capable of binding the MuSK receptor. In specific embodiments, the MuSK-specific ligand is agrin or a fragment or derivative thereof capable of binding MuSK, or an anti-MuSK antibody or fragment or derivative thereof, including, for example, an scFv.

In other specific embodiments, the muscle-targeting ligand of the muscle-targeting fusion polypeptide comprises three or more muscle cadherin (M-cadherin) extracellular cadherin domains, or derivatives or fragments thereof, capable of binding specifically to a muscle cells or other cells that express homophilic muscle cadherins. In one specific embodiment, the muscle-targeting ligand consists essentially of the first three (3) or four (4) N-terminal extracellular domains of M-cadherin.

The active or therapeutic agent may be any agent that is desirable to deliver to a pre-selected site for therapeutic purposes. In specific embodiments, the active or therapeutic agent is a ligand for a second cell surface receptor, and is capable of binding and activating a second receptor. In other embodiments, the active or therapeutic agent is an agent capable of blocking the activity of another agent that is active on the target cell. In a specific embodiment, the active or therapeutic agent is selected from the group consisting of IL-15, myotrophin, urocortin, urocortin II, a natural or mutant IGF-1 or IGF-2, insulin, the pro domain of myostatin, hGH, proliferin, follistatin, FSTL1, and FLRG, and a biologically active fragments thereof.

In one specific embodiment, the invention provides a muscle-targeting fusion polypeptide, comprising (i) agrin, or a fragment or derivative thereof capable of binding the MuSK receptor; and (ii) an active or therapeutic agents selected from the group consisting of IL-15, myotrophin, urocortin, urocortin II, a natural or mutant IGF-1 or IGF-2, insulin, the pro domain of myostatin, hGH, proliferin, follistatin, FSTL1, and FLRG, or a biologically active fragment thereof; and optionally (iii) a multimerizing component, and/or (iv) a signal sequence. In another specific embodiment, the invention provides a muscle-targeting fusion polypeptide comprising (i) three (3) N-terminal extracellular domains of M cadherin; and (ii) an active or therapeutic agents selected from the group consisting of IL-15, myotrophin, urocortin, urocortin II, a natural or mutant IGF-1 or IGF-2, insulin, the pro domain of myostatin, hGH, proliferin, follistatin, FSTL1, and FLRG, or a biologically active fragment thereof; and optionally (iii) a multimerizing component, and/or (iv) a signal sequence.

In a separate embodiment, the invention provides composition for delivering two active or therapeutic agents. The two active or therapeutic agents may act synergistically when present together. Accordingly, in a third aspect, the invention features a fusion polypeptide comprising (i) a first active or therapeutic agent, and (ii) a second active or therapeutic agent. In specific embodiments, the fusion polypeptide optionally further comprises (iii) a multimerizing component capable of forming a multimer with another targeting fusion polypeptide, and/or (iv) a signal sequence. In a preferred embodiment, one active or therapeutic agent is natural or mutant human growth hormone (hGH) or proliferin, or a biologically active fragment thereof and the other agent is natural or mutant IGF-1 or IGF-2, or a biologically active fragment thereof.

In another embodiment, the invention provides compositions for delivering IGF-related polypeptides, which may be used alone or as a components of the targeting or therapeutic fusion molecules described herein. Such polypeptides comprise a mutant IGF-1 or IGF-2 molecule having (i) deletion of the first three amino acids (Δ3), or substitution of either arginine (R) or alanine (A) for glutamic acid (E) at position 3 (E3R or E3A); and (ii) modification in the double arginines (RR) at positions 36 and 37 by either substitution of an alanine (A) for an arginine (A) at position 36 or 37 or deletion of R36(del36) or R37(del37); wherein the IGF-derived polypeptides optionally comprise (iii) a multimerizing component capable of forming a multimer with another IGF-related polypeptide, and/or (iv) a signal sequence.

In other embodiment, the invention provides compositions for delivering myostatin-inhibiting fusion polypeptides, which may be used alone or as components of the targeting or therapeutic fusion molecules described herein. Such compositions comprise the propeptide of human myostatin. In one specific embodiment, the fusion proteins comprise the propeptide of myostatin fused to a multimerizing component, such as the Fc domain of IgG.

In a fourth aspect, the invention features a targeting fusion polypeptide comprising (i) a targeting ligand, or derivative or fragment thereof, capable of binding specifically to a pre-selected cell surface protein, (ii) a first active or therapeutic agent, and (ii) a second active or therapeutic agent. In specific embodiments, the fusion polypeptide optionally further comprises (iii) a multimerizing component capable of forming a multimer with another targeting fusion polypeptide, and/or (iv) a signal sequence. In a preferred embodiment, one active or therapeutic agent is natural or mutant human growth hormone (hGH) or proliferin, or a biologically active fragment thereof and the other agent is natural or mutant IGF-1 or IGF-2, or a biologically active fragment thereof. In one preferred embodiment, the targeting ligand is agrin, one active agent is IGF1 or mutant thereof, and one active agent is hGH, such as in the targeting fusion polypeptides of SEQ ID NOS:23-26.

In one embodiment, the targeting fusion polypeptide is a muscle-targeting fusion polypeptide, comprising (i) a targeting ligand, or derivative or fragment thereof, capable of binding specifically to a muscle cell surface protein, (ii) a first active or therapeutic agent, and (ii) a second active or therapeutic agent, optionally further comprises (iii) a multimerizing component capable of forming a multimer with another targeting fusion polypeptide, and/or (iv) a signal sequence. In a preferred embodiment, one active or therapeutic agent is natural or mutant human growth hormone (hGH), or a biologically active fragment thereof and another active or therapeutic agent is natural or mutant IGF-1 or IGF-2, or a biologically active fragment thereof.

In a specific embodiment, the muscle-targeting fusion polypeptide comprises (i) agrin, or a fragment or derivative thereof capable of binding the MuSK receptor; and (ii) a first active or therapeutic agent, wherein the first active or therapeutic agent is natural or mutant human growth hormone or a biologically active fragment thereof; (iii) a second active or therapeutic agent, wherein the second active or therapeutic agent is natural or mutant IGF-1 or IGF-2, or a biologically active fragment thereof; and optionally (iv) a multimerizing component, and/or (v) a signal sequence. In another embodiment, the muscle-targeting fusion polypeptide comprises a sequence selected from the group consisting of SEQ ID NOS: 9-31. In preferred embodiments, the muscle-targeting fusion polypeptide comprises a sequence selected from the group consisting of SEQ ID NOS:26-29.

In a fifth aspect, the invention provides an IGF-related polypeptide comprising a mutant IGF-1 or IGF-2 molecule having (i) deletion of the first three amino acids (Δ3), or substitution of either arginine (R) or alanine (A) for glutamic acid (E) at position 3; and (ii) modification in the double arginines (RR) at positions 36 and 37 by either substitution of an alanine (A) at position 36 or position 37 or deletion or R36 or R37; wherein the IGF-derived polypeptides optionally comprise (iii) a multimerizing component capable of forming a multimer with another IGF-related polypeptide, and/or (iv) a signal sequence.

In a sixth aspect, the invention provides a fusion polypeptide comprising the propeptide of human myostatin fused to a multimerizing component, such as the Fc domain of IgG.

In specific embodiments wherein the fusion polypeptides of the invention comprise a multimerizing component, the multimerizing component may be selected from the group consisting of (i) a multimerizing component comprising a cleavable region (C-region), (ii) a truncated multimerizing component, (iii) an amino acid sequence between 1 to about 500 amino acids in length, optionally comprising at least one cysteine residue, (iv) a leucine zipper, (v) a helix loop motif, (vi) a coil-coil motif, (vii) an Fc-protein, and (viii) a combination thereof. In specific embodiments in which the targeting fusion polypeptide comprises a signal sequence, the signal sequence may comprise any sequence known to a skilled artisan for directing secretion of a polypeptide or protein from a cell, include natural or synthetic sequences. Generally, a signal sequence is placed at the beginning or amino-terminus of the fusion polypeptide of the invention. Such a signal sequence may be native to the cell, recombinant, or synthetic.

The components of the fusion polypeptides of the invention may be connected directly to each other or connected via one or more spacer sequences. In one preferred embodiment, the components are fused directly to each other. In another preferred embodiment, the components are connected with a nucleic acid sequence encoding a spacer of 1-200 amino acids. Any spacer known to the art may be used to connect the polypeptide components. A spacer sequence may also include a sequence used to enhance expression of the fusion polypeptide, provide restriction sites, and allow component domains to form optimal tertiary and quaternary structures and/or to enhance the interaction of a component with its receptor. In one embodiment, the fusion polypeptide of the invention comprises one or more peptide sequences between one or more components which is (are) between 1-25 amino acids.

The components of the fusion polypeptide of the invention may be arranged in a variety of configurations. For example, the targeting ligand component (1), the active or therapeutic agent(s) component (2), and the optional multimerizing component (3) may be arranged in one of the following configurations: 1-2; 2-1; 1-2-3; 1-3-2; 3-1-2; 2-1-3; 2-3-1, or 3-2-1. Still further, multiple components of a targeting ligand or active agent may be included in the fusion polypeptide, e.g., 1-1-2, 2-1-1, 1-2-1, 2-2-1, 1-1-2-1-1, etc.

When the active or therapeutic agent(s) component of the fusion polypeptide of the invention comprises two active or therapeutic agents, these agents may be arranged in a variety of configurations. For example, active agent (1) and agent (2) may be arrange either 1-2 or 2-1. Still further, the same agent may be included more than once in the component, e.g., 1-1-2; 1-2-2; 1-2-1, etc.

In a seventh aspect, the invention provides nucleic acid molecules encoding the fusion polypeptides of the invention.

In related aspects, the invention features a vector comprising a nucleic acid molecule of the invention, including expression vectors comprising the nucleic acid molecules operatively linked to an expression control sequence, and host-vector systems for the production of a fusion polypeptide which comprise the expression vector, in a suitable host cell; host-vector systems wherein the suitable host cell is, without limitation, a bacterial, yeast, insect, or mammalian cell. Examples of suitable cells include E. coli, B. subtilis, BHK, COS and CHO cells. Additionally encompassed are fusion polypeptides of the invention modified by acetylation or pegylation. Methods for acetylating or pegylating a protein are well known in the art.

The invention further provides a method of producing a fusion polypeptide of the invention, comprising culturing a host cell transfected with a vector comprising a nucleic acid molecule of the invention, under conditions suitable for expression of the protein from the host cell, and recovering the polypeptide so produced.

The invention features therapeutic methods for the treatment of a disease or condition, comprising administering a therapeutically effective amount of a fusion protein of the invention to a subject in need thereof, or a subject at risk for development of that disease or condition. When the disease or condition is a muscle condition, such as atrophy, the therapeutic method of the invention comprises administering a therapeutically effective amount of a muscle-targeting fusion protein of the invention to a subject in need thereof, wherein the muscle-related disease or condition is ameliorated or inhibited. In one specific embodiment, the invention features a method of inhibiting or ameliorating muscle atrophy, comprising administering a therapeutically effective amount of a fusion polypeptide comprising IGF-1 and agrin, or biologically active fragments or derivatives of IGF-1 and/or agrin, wherein IGF-1 is specifically delivered to the desired site by agrin binding to the muscle-specific surface receptor MuSK. In another embodiment, the muscle-specific fusion polypeptide comprises agrin and IL-15, or biologically active fragments or derivatives of agrin and/or IL-15. In another embodiment, the muscle-specific fusion polypeptide comprises agrin; natural or mutant hGH, or a biologically active fragment or a derivative thereof; and natural or mutant IGF-1, or a biologically active fragment or a derivative thereof. In yet another embodiment, the muscle-specific fusion polypeptide comprises agrin; natural or mutant hGH, or a biologically active fragment or a derivative thereof; and natural or mutant IGF-2, or a biologically active fragment or a derivative thereof. The muscle-related condition or disorder treated by the fusion polypeptides of the invention may arise from a number of sources, including for example: denervation; degenerative, metabolic or inflammatory neuropathy; infantile and juvenile spinal muscular atrophies; autoimmune motor neuropathy; from chronic disease, including cachexia resulting from cancer, AIDS, fasting or rhabdomyolysis; and from muscular dystrophy syndromes such as Duchenne.

Accordingly, in a seventeenth aspect, the invention features pharmaceutical compositions comprising a targeting fusion protein of the invention with a pharmaceutically acceptable carrier. Such pharmaceutical compositions may comprise the fusion proteins or nucleic acids which encode them. In specific embodiments, the pharmaceutical composition of the invention comprises a muscle-targeting polypeptide comprising (i) agrin, or a biologically active fragment or derivative thereof, capable of binding the muscle-specific surface protein MuSK, and (ii) an active agent selected from the group consisting of insulin like growth factor 1 (IGF-1) and interleukin-15 (IL-15), optionally further comprising (iii) a multimerizing component, together with a pharmaceutically acceptable carrier. In another embodiment, the pharmaceutical composition of the invention comprises a muscle-targeting polypeptide comprising (i) agrin, or a fragment or derivative thereof capable of binding the MuSK receptor; and (ii) a first active or therapeutic agent, wherein the first active or therapeutic agent is natural or mutant human growth hormone or proliferin, or a biologically active fragment thereof; (iii) a second active or therapeutic agent, wherein the second active or therapeutic agent is natural or mutant IGF-1 or IGF-2, or a biologically active fragment thereof; and optionally (iv) a multimerizing component, together with a pharmaceutically acceptable carrier.

The invention features a method of activating and/or phosphorylation multiple cell surface receptors simultaneously, by providing a fusion polypeptide capable of binding multiple cell surface receptor to a cell expressing multiple receptors. In one embodiment, the invention features a fusion polypeptide capable of binding both MuSK and IGF-R. In another embodiment, the invention provides a fusion polypeptide capable of binding both GHR and IFG-R. In yet another embodiment, the invention provides a fusion polypeptide capable of binding MuSK, GHR, and IGF-R simultaneously. Preferably, the method of the invention is achieved by providing a targeting fusion polypeptide described above.

Other objects and advantages will become apparent from a review of the ensuing detailed description.

DETAILED DESCRIPTION

Before the present methods are described, it is to be understood that this invention is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus for example, references to “a method” include one or more methods, and/or steps of the type described herein and/or which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.

General Description

The invention encompasses fusion polypeptides and nucleic acids that encode them which comprise one or more active or therapeutic agent(s). The invention further provides targeting fusion polypeptides and nucleic acids which encode then comprise a targeting ligand that specifically binds a pre-selected cell surface protein, such as a receptor, and one or more active or therapeutic agent(s) capable of achieving a desired effect when delivered to the desired cell or tissue.

Definitions

“Biologically active” fragments or derivatives of a targeting ligand or an active or therapeutic component of the targeting fusion polypeptides of the invention encompass any naturally occurring molecule, or mutant or derivative thereof capable of achieving the desired effect at the target site. For example, when the active or therapeutic agent is IGF-1, the invention envisions the use of a mutant or derivative IGF-1 molecule capable of binding the IGF-1 receptor. Examples of such mutants, which retain the activity of the native molecule but which have greater stability and potency, are described herein. A “biologically active” fragment of derivative of any targeting component is any portion or mutant thereof capable of binding the target cell. Thus, for example, when the targeting ligand is agrin, a biologically active fragment or derivative is any portion or mutant of agrin capable of binding the MuSK receptor.

The terms “treatment”, “treating”, and the like are used herein to generally mean obtaining a desired pharmacologic and/or physiologic effect. The effect may be prophylactic in terms of completely or partially preventing a disease, condition, or symptoms thereof, and/or may be therapeutic in terms of a partial or complete cure for a disease or condition and/or adverse effect attributable to the disease or condition. “Treatment” as used herein covers any treatment of a disease or condition of a mammal, particularly a human, and includes: (a) preventing the disease or condition from occurring in a subject which may be predisposed to the disease or condition but has not yet been diagnosed as having it; (b) inhibiting the disease or condition, i.e., arresting its development; or (c) relieving the disease or condition, i.e., causing regression of the disease or condition. The population of subjects treated by the method of the disease includes subject suffering from the undesirable condition or disease, as well as subjects at risk for development of the condition or disease.

By the term “therapeutically effective dose” is meant a dose that produces the desired effect for which it is administered. The exact dose will depend on the purpose of the treatment, and will be ascertainable by one skilled in the art using known techniques (see, for example, Lloyd (1999) The Art, Science and Technology of Pharmaceutical Compounding).

As used herein, a “condition or disease” generally encompasses a condition of a mammalian host, particularly a human host, which is undesirable and/or injurious to the host. Thus, treating a muscle-related condition with a fusion polypeptide which specifically targets skeletal muscle will encompass the treatment of a mammal, in particular, a human, who has symptoms reflective of decreased target muscle receptor activation, or who is expected to have such decreased levels in response to a disease, condition or treatment regimen. Treating a muscle-related condition or disease encompasses the treatment of a human subject wherein enhancing the activation of a target muscle receptor with the muscle specific fusion polypeptide of the invention results in amelioration of an undesirable symptom resulting from the muscle-related condition or disease. As used herein, a “muscle-related condition” also includes a condition in which it is desirable to alter, either transiently, or long-term, activation of a particular target muscle receptor.

Targeting Fusion Polypeptide Components

The first component of the targeting fusion polypeptides of the invention is a targeting ligand. A targeting ligand is a molecule, e.g., a protein or fragment thereof that specifically binds with high affinity to a target on a pre-selected cell, such as a surface protein such as a receptor that is present to a greater degree on the pre-selected cell target than on any other body tissue. For example, as described in U.S. Pat. Nos. 5,814,478 and 6,413,740, the MuSK receptor is highly specific to muscle. Accordingly, the cognate ligand agrin, as well as MuSK binding portions thereof is an example of a targeting ligand useful as a first component in the fusion polypeptides of the present invention. Another example of a targeting ligand is a group of cadherin domains from a human cadherin. Accordingly, human cadherin domains from, for example, human muscle cadherin may be used in the targeting fusion polypeptides of the invention to target muscle cells. The targeting ligand component of the fusion polypeptide of the invention may include a naturally occurring or engineered ligand, or a fragment thereof, capable of binding the pre-selected target cell.

In another embodiment of the invention, the first component targeting ligand of the targeting fusion polypeptides of the invention consists of at least three, four or five cadherin domains, or derivatives or fragments thereof, capable of binding specifically to target cells that express homophilic cadherins. By the term “cadherin” is meant a molecule that is a member of a family of calcium-dependent cell-cell adhesion molecules consisting of several distinct proteins. Several human cadherins have been identified and characterized, including, but not limited to, vascular endothelial cadherin (VE-cadherin; Ludwig et al. (2000) Mamm. Genome 11 (11): 1030-1033), nerve cadherin (N-cadherin; Reid et al. (1990) J. Nucleic Acids Res. 18 (19), 5896), muscle cadherin (M-cadherin; Shimoyama et al. (1998) J. Biol. Chem. 273(16): 10011-10018; Shibata et al. (1997) J. Biol. Chem. 272(8):5236-5270), liver-intestine cadherin (Cadherin-17; Dantzig et al. (1994) Science 264(5157):430-433), heart cadherin (Cadherin-13; Tanihara et al. (1994) Cell Adhes. Commun. 2(1):15-26), tissue-lung cadherin (Cadherin-26; Ota et al. (2004) Nat. Genet. 36(1):40-45), Cadherin-24 (Katafiasz et al. (2003) J. Biol. Chem. 278(30):27513-27519; Clark et al. (2003) Genome Res. 13(10):2265-2270), and epithelial cadherin (E-cadherin; Cadherin-1; Bussemakers et al. (1993) Mol. Biol. Rep. 17(2):123-128).

Typically, each cadherin molecule consists of an extracellular domain, which consists of five (5) cadherin domains, as well as a transmembrane domain and intracellular domain. The extracellular cadherin domains interact with homophilic cadherins on adjacent cells, thus cadherins act as both ligands and receptors. Cadherins are also believed to exclude or repel heterophilic cadherins on adjacent cells. A common feature of human cadherins is the presence of 5 tandomly repeated cadherin domains. Such cadherin domains bind to homophilic cadherin domains on adjacent cells, thus causing cell-cell adhesion.

As described herein, applicants have discovered that the ability of cadherin domains to attract homophilic cadherins can be used to create targeting molecules that are directed to specific cell types. Further, such cell-cell adhesion can be mimicked using a minimum of three and up to five cadherin domains from any human cadherin. Accordingly, constructs are provided which utilize the specificity of cadherin domains to target the fusion polypeptides of the invention to specific cells. Thus, for example, if the desired target is muscle tissue, a fusion polypeptide of the invention would comprise at least three cadherin domains from the extracellular domain of human M-cadherin (or biologically active fragments or derivatives thereof that are capable of binding homophilic M-cadherin), fused to a second component that is active on muscle cells. Alternatively, if the desired target were heart tissue, the first component would comprise at least three cadherin domains from the extracellular domain of H-cadherin, or biologically active fragments or derivatives thereof that are capable of binding homophilic H-cadherin.

Further examples of targeting ligands also include, but are not limited to, antibodies and portions thereof that bind a pre-selected cells surface protein with high affinity. By “high affinity” is meant an equilibrium dissociation constant of at least 10⁻⁷ molar, as determined by assay methods known in the art, for example, BiaCore analysis. In one embodiment, the targeting ligand component of the targeting fusion polypeptides of the invention may also comprise one or more immunoglobulin binding domains isolated from antibodies generated against a selected tissue-specific surface protein or target tissue-specific receptor. The term “immunoglobulin or antibody” as used herein refers to a mammalian, including human, polypeptide comprising a framework region from an immunoglobulin gene or fragments thereof that specifically binds and recognizes an antigen, which, in the case of the present invention, is a tissue-specific surface protein, a target tissue-specific receptor, or portion thereof. If the intended targeting fusion polypeptide will be used as a mammalian therapeutic, immunoglobulin binding regions should be derived from the corresponding mammalian immunoglobulins. If the targeting fusion polypeptide is intended for non-therapeutic use, such as for diagnostics and ELISAs, the immunoglobulin binding regions may be derived from either human or non-human mammals, such as mice. The human immunoglobulin genes or gene fragments include the kappa, lambda, alpha, gamma, delta, epsilon, and mu constant regions, as well as the myriad immunoglobulin variable region genes. Light chains are classified as either kappa or lambda. Heavy chains are classified as gamma, mu, alpha, delta, or epsilon, which in turn define the immunoglobulin classes, IgG, IgM, IgA, IgD, and IgE, respectively. Within each IgG class, there are different isotypes (e.g. IgG₁, IgG₂, etc.). Typically, the antigen-binding region of an antibody will be the most critical in determining specificity and affinity of binding.

An exemplary immunoglobulin (antibody) structural unit of human IgG, comprises a tetramer. Each tetramer is composed of two identical pairs of polypeptide chains, each pair having one light chain (about 25 kD) and one heavy chain (about 50-70 kD). The N-terminus of each chain defines a variable region of about 100-110 or more amino acids primarily responsible for antigen recognition. The terms “variable light chain” (V_(L)) and variable heavy chain (V_(H)) refer to these light and heavy chains respectively.

Antibodies exist as intact immunoglobulins, or as a number of well-characterized fragments produced by digestion with various peptidases. For example, pepsin digests an antibody below the disulfide linkages in the hinge region to produce F(ab)′₂, a dimer of Fab which itself is a light chain joined to V_(H)-C_(H) by a disulfide bond. The F(ab)′₂ may be reduced under mild conditions to break the disulfide linkage in the hinge region, thereby converting the F(ab)′₂ dimer into an Fab′ monomer. The Fab′ monomer is essentially Fab with part of the hinge region. While various antibody fragments are defined in terms of the digestion of an intact antibody, one of skill will appreciate that such fragments may be synthesized de novo either chemically or by using recombinant DNA methodology. Thus, the terms immunoglobulin or antibody, as used herein, also includes antibody fragments either produced by the modification of whole antibodies, or those synthesized de novo using recombinant DNA methodologies (e.g., single chain Fv)(scFv)) or those identified using phase display libraries (see, for example, McCafferty et al. (1990) Nature 348:552-554). In addition, the fusion polypeptides of the invention include the variable regions of the heavy (V_(H)) or the light (V_(L)) chains of immunoglobulins, as well as tissue-specific surface protein and target receptor-binding portions thereof. Methods for producing such variable regions are described in Reiter, et al. (1999) J. Mol. Biol. 290:685-698.

Methods for preparing antibodies are known to the art. See, for example, Kohler & Milstein (1975) Nature 256:495-497; Harlow & Lane (1988) Antibodies: a Laboratory Manual, Cold Spring Harbor Lab., Cold Spring Harbor, N.Y.). The genes encoding the heavy and light chains of an antibody of interest can be cloned from a cell, e.g., the genes encoding a monoclonal antibody can be cloned from a hybridoma and used to produce a recombinant monoclonal antibody. Gene libraries encoding heavy and light chains of monoclonal antibodies can also be made from hybridoma or plasma cells. Random combinations of the heavy and light chain gene products generate a large pool of antibodies with different antigenic specificity. Techniques for the production of single chain antibodies or recombinant antibodies (U.S. Pat. Nos. 4,946,778; 4,816,567) can be adapted to produce antibodies used in the fusion polypeptides and methods of the instant invention. Also, transgenic mice, or other organisms such as other mammals, may be used to express human or humanized antibodies. Alternatively, phage display technology can be used to identify antibodies, antibody fragments, such as variable domains, and heteromeric Fab fragments that specifically bind to selected antigens.

Screening and selection of preferred immunoglobulins (antibodies) can be conducted by a variety of methods known to the art. Initial screening for the presence of monoclonal antibodies specific to a tissue-specific or target receptor may be conducted through the use of ELISA-based methods or phage display, for example. A secondary screen is preferably conducted to identify and select a desired monoclonal antibody for use in construction of the tissue-specific fusion polypeptides of the invention. Secondary screening may be conducted with any suitable method known to the art. One preferred method, termed “Biosensor Modification-Assisted Profiling” (“BiaMAP”) is described in U.S. patent publication 2004/101920, herein specifically incorporated by reference in its entirety. BiaMAP allows rapid identification of hybridoma clones producing monoclonal antibodies with desired characteristics. More specifically, monoclonal antibodies are sorted into distinct epitope-related groups based on evaluation of antibody: antigen interactions.

Active or Therapeutic Agent

Another component of the fusion polypeptides of the invention is an active or therapeutic agent or mutant or derivative thereof, i.e. a molecule capable of having a desired effect when delivered to the pre-selected target site, e.g., cell or tissue, Active or therapeutic agents, include, but are not limited to, small molecules, hormones, growth factors, therapeutic biologics, activating antibodies and portions thereof, and blocking antibodies and portions thereof, that are capable of having a desirable effect upon delivery to a target cell or tissue.

In particular embodiments wherein the targeting fusion polypeptide is directed at muscle cells or tissue, the fusion polypeptide comprises a targeting ligand, and a therapeutic agent that is active on muscle cells. Such agents include, but are not limited to, insulin, IL-15, myotrophin, urocortin, urocortin II, human myostatin propeptide, IGF-1, hGH, proliferin, follistatin, FSTL1, and FLRG, or mutants, derivative, or fragments thereof having biologically activity. In addition, the active or therapeutic agent may comprise a blocking antibody or biologically active derivative thereof, which blocks, for example, myostatin, activin receptor, BMP receptor 1, TNF receptor and IL-1 receptor. Alternatively, the active or therapeutic agent may comprise an activating antibody that activates, for example, the IFG1 receptor, B2adrenergic receptor or the IL-15 receptor complex.

In embodiments wherein the targeting fusion polypeptide is directed at vascular endothelial cells, the fusion polypeptide comprises a targeting ligand, for example, at least 3 cadherin domains of human VE-cadherin and a therapeutic agent that is active on endothelial cells, such as angiopoietin or VEGF, or activating or blocking antibodies or portions thereof.

Optional Multimerizing Component

In specific embodiments, the fusion polypeptides of the invention comprise a multimerizing component. A multimerizing component includes any natural or synthetic sequence capable of interacting with another multimerizing component to form a higher order structure, e.g., a dimer, a trimer, etc. The multimerizing component may be selected from the group consisting of (i) a multimerizing component comprising a cleavable region (C-region), (ii) a truncated multimerizing component, (iii) an amino acid sequence between 1 to about 500 amino acids in length, (iv) a leucine zipper, (v) a helix loop motif, and (vi) a coil-coil motif. When the multimerizing component comprises an amino acid sequence between 1 to about 500 amino acids in length, the sequence may contain one or more cysteine residues capable of forming a disulfide bond with a corresponding cysteine residue on another fusion polypeptide comprising a multimerizing component with one or more cysteine residues. In some embodiments, the multimerizing component comprises an immunoglobulin-derived domain from, for example, human IgG, IgM or IgA, or comparable immunoglobulin domains from other animals, including, but not limited to, mice. In specific embodiments, the immunoglobulin-derived domain may be selected from the group consisting of the constant region of IgG, the Fc domain of IgG, an Fc-protein, the heavy chain of IgG, and the light chain of IgG. The Fc domain of IgG may be selected from the isotypes IgG1, IgG2, IgG3, and IgG4, as well as any allotype within each isotype group.

Optional Component Spacers

The components of the targeting fusion polypeptides of the invention may be connected directly to each other or be connected via spacers. The term “spacer” or “linker” means one or more molecules, e.g., nucleic acids or amino acids, or non-peptide moieties, such as polyethylene glycol, which may be inserted between one or more component domains. For example, spacer sequences may be used to provide a restriction site between components for ease of manipulation. A spacer may also be provided to enhance expression of the fusion polypeptide from a host cell, to decrease steric hindrance such that the component may assume its optimal tertiary or quaternary structure and/or interact appropriately with its target molecule. For spacers and methods of identifying desirable spacers, see, for example, George et al. (2003) Protein Engineering 15:871-879, herein specifically incorporated by reference.

A spacer sequence may include one or more amino acids naturally connected to a receptor component, or may be an added sequence used to enhance expression of the fusion protein, provide specifically desired sites of interest, allow component domains to form optimal tertiary structures and/or to enhance the interaction of a component with its target molecule. In one embodiment, the spacer comprises one or more peptide sequences between one or more components which is (are) between 1-100 amino acids, preferably 1-25. In one specific embodiment, the spacer is a three amino acid sequence; more specifically, the three amino acid sequence of Gly Pro Gly.

Nucleic Acid Construction and Expression

Individual components of the fusion polypeptides of the invention may be produced from nucleic acids molecules using any suitable method known in the art. The nucleic acids encode fusion polypeptides which comprise one or more active or therapeutic agent(s). The nucleic acids encode targeting fusion polypeptides which comprise (i) a component that comprises a ligand or derivative or fragment thereof that binds a tissue-specific receptor, (ii) a component that comprises one or more agent(s) capable of providing a therapeutic effect or activating the target tissue, and optionally, (iii) a multimerizing component, wherein the multimerizing component multimerizes with a multimerizing component on another fusion polypeptide to form a multimeric tissue-specific fusion protein of the invention. The nucleic acid molecules can be inserted into a vector that is able to express the fusion polypeptides when introduced into an appropriate host cell. Appropriate host cells include, but are not limited to, bacterial, yeast, insect, and mammalian cells. Any of the methods known to one skilled in the art for the insertion of DNA fragments into a vector may be used to construct expression vectors encoding the fusion polypeptides of the invention under control of transcriptional/translational control signals. These methods may include in vitro recombinant DNA and synthetic techniques and in vivo recombinations (See Sambrook et al. Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory; Current Protocols in Molecular Biology, Eds. Ausubel, et al., Greene Publ. Assoc., Wiley-Interscience, N.Y.).

Expression of the nucleic acid molecules of the invention may be regulated by a second nucleic acid sequence so that the molecule is expressed in a host transformed with the recombinant DNA molecule. For example, expression of the nucleic acid molecules of the invention may be controlled by any promoter/enhancer element known in the art. Promoters which may be used to control expression of the fusion polypeptide molecules include, but are not limited to, the long terminal repeat as described in Squinto et al. (1991) Cell 65:1-20; the SV40 early promoter region, the CMV promoter, the M-MuLV 5′ terminal repeat the promoter contained in the 3′ long terminal repeat of Rous sarcoma virus, the herpes thymidine kinase promoter, the regulatory sequences of the metallothionine gene; prokaryotic expression vectors such as the b-lactamase promoter, or the tac promoter (see also “Useful proteins from recombinant bacteria” in Scientific American (1980) 242:74-94); promoter elements from yeast or fungi such as the Gal 4 promoter, the ADH (alcohol dehydrogenase) promoter, PGK (phosphoglycerol kinase) promoter, alkaline phosphatase promoter, and tissue-specific transcriptional control regions derived from elastase I gene, insulin gene, immunoglobulin gene, mouse mammary tumor virus, albumin gene, α-fetoprotein gene, α1-antitrypsin gene, β-globin gene, myelin basic protein gene, myosin light chain-2 gene, and gonadotropic releasing hormone gene.

In accordance with the invention, the nucleic acid constructs may include components which are derived from immunoglobulins (antibodies). In general, such components will be derived from heavy (V_(H)) or light (V_(L)) chain variable regions. After identification and selection of antibodies exhibiting the desired binding characteristics, the variable regions of the heavy chains and/or light chains of each antibody is isolated, amplified, cloned and sequenced. Modifications may be made to the V_(H) and V_(L) nucleotide sequences, including additions of nucleotide sequences encoding amino acids and/or carrying restriction sites, deletions of nucleotide sequences encoding amino acids, or substitutions of nucleotide sequences encoding amino acids.

After identification of such ligands or portions thereof exhibiting desired characteristics, the nucleic acids that encode such domains are used in the nucleic acid constructs. Such nucleic acids may be modified, including additions of nucleotide sequences encoding amino acids and/or carrying restriction sites, deletions of nucleotide sequences encoding amino acids, or substitutions of nucleotide sequences encoding amino acids.

The nucleic acid constructs of the invention are inserted into an expression vector or viral vector by methods known to the art, wherein the nucleic acid molecule is operatively linked to an expression control sequence. Also provided is a host-vector system for the production of a tissue-specific fusion polypeptide of the invention, which comprises the expression vector of the invention, which has been introduced into a host cell suitable for expression of the fusion polypeptide. The suitable host cell may be a bacterial cell such as E. coli, a yeast cell, such as Pichia pastoris, an insect cell, such as Spodoptera frugiperda, or a mammalian cell, such as a COS, CHO, 293, BHK or NSO cell.

The invention further encompasses methods for producing the fusion polypeptides of the invention by growing cells transformed with an expression vector under conditions permitting production of the tissue-specific fusion polypeptides and recovery of the fusion polypeptides so produced. Cells may also be transduced with a recombinant virus comprising the nucleic acid construct of the invention.

The fusion polypeptides may be purified by any technique, which allows for the subsequent formation of a stable polypeptide. For example, and not by way of limitation, the fusion polypeptides may be recovered from cells either as soluble polypeptides or as inclusion bodies, from which they may be extracted quantitatively by 8M guanidinium hydrochloride and dialysis. In order to further purify the fusion polypeptides, conventional ion exchange chromatography, hydrophobic interaction chromatography, reverse phase chromatography or gel filtration may be used. The fusion polypeptides may also be recovered from conditioned media following secretion from eukaryotic or prokaryotic cells.

In one embodiment of the invention, cells expressing a targeting fusion polypeptide of the invention are selected having a desired high production rate. A variety of selection processes known to the art may be used.

Screening and Detection Methods

The fusion polypeptides of the invention may also be used in in vitro or in vivo screening methods where it is desirable to detect and/or measure target protein levels or, for example, levels of receptor-bearing cells. Screening methods are well known to the art and include cell-free, cell-based, and animal assays. In vitro assays can be either solid state or soluble. Receptor detection may be achieved in a number of ways known to the art, including the use of a label or detectable group capable of identifying a tissue-specific polypeptide which is bound to a target cell. Detectable labels are well developed in the field of immunoassays and may generally be used in conjunction with assays using the tissue-specific fusion polypeptide of the invention.

A fusion polypeptide of the invention may also be directly or indirectly coupled to a label or detectable group when desirable for the purpose it is being used. A wide variety of labels may be used, depending on the sensitivity required, ease of conjugation, stability requirements, available instrumentation, and disposal provisions.

Therapeutic Methods

The invention herein further provides for the development of muscle-targeting fusion polypeptide described herein as a therapeutic for the treatment of patients suffering from disorders involving muscle cells or tissue which express any target muscle receptor. For example, a decrease in muscle mass, or atrophy, is associated with various physiological and pathological states. For example, muscle atrophy can result from denervation due to nerve trauma; degenerative, metabolic or inflammatory neuropathy, e.g. Guillian-Barre syndrome; peripheral neuropathy; or nerve damage caused by environmental toxins or drugs. Muscle atrophy may also result from denervation due to a motor neuropathy including, for example, adult motor neuron disease, such as Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig's disease); infantile and juvenile spinal muscular atrophies; and autoimmune motor neuropathy with multifocal conductor block. Muscle atrophy may also result from chronic disease resulting from, for example, paralysis due to stroke or spinal cord injury; skeletal immobilization due to trauma, such as, for example, fracture, ligament or tendon injury, sprain or dislocation; or prolonged bed rest. Metabolic stress or nutritional insufficiency, which may also result in muscle atrophy, include the cachexia of cancer and other chronic illnesses including AIDS, fasting or rhabdomyolysis, and endocrine disorders such as disorders of the thyroid gland and diabetes. Muscle atrophy may also be due to a muscular dystrophy syndromes such as Duchenne, Becker, myotonic, fascioscapulohumeral, Emery-Dreifuss, oculopharyngeal, scapulohumeral, limb girdle, and congenital types, as well as the dystrophy known as Hereditary Distal Myopathy. Muscle atrophy may also be due to a congenital myopathy, such as benign congenital hypotonia, central core disease, nemalene myopathy, and myotubular (centronuclear) myopathy. Muscle atrophy also occurs during the aging process. Muscle atrophy in various pathological states is associated with enhanced proteolysis and decreased production of muscle proteins. Follistatin and related molecule FSTL1 and FLRG have been shown to block myostatin-a secreted protein that inhibits muscle growth. Myostatin-inhibitors have been suggested to be useful to increase muscle mass and to treat myopathy diseases (Bogdanovitch, et al. (2002) Nature 420:418-421.) Accordingly, a muscle-targeting fusion protein of the invention, wherein the active agent is folllistatin, FSTL-1 or FLRG or a related myostatin-blocking molecule would be useful to increase muscle mass or to treat myopathy diseases. In addition, human myostatin propeptide, which also blocks myostatin, may be used to treat these diseases.

The ability of the targeting fusion proteins of the invention to exhibit a high degree of specificity for pre-selected target surface proteins makes them therapeutically useful for efficiently treating and/or activating a protein(s) at a desired pre-selected site. For example, the utility of IGF-1 for the treatment of a muscle-related condition, such as atrophy has, to date, been limited due to the presence of the IGF-1 receptor in non-muscle tissue. A muscle-specific fusion polypeptide of the invention wherein the ligand specific for a muscle surface protein is agrin or a MuSK-binding fragment thereof, and the active and/or therapeutic agent is IGF-1 or fragment thereof has high degree of specificity for muscle tissue. IGF-I has been used to treat humans suffering from growth hormone deficiencies, tissue wasting including burns, skeletal trauma, infection, cancer, cystic fibrosis, Duchenne muscular dystrophy, Becker dystrophy, autosomal recessive dystrophy, polymyositis, as well as myopathies and AIDS (U.S. Pat. No. 5,622,932).

Methods of Administration

Methods known in the art for the therapeutic delivery of agents such as proteins or nucleic acids can be used for the therapeutic delivery of a fusion polypeptide or a nucleic acid encoding a fusion polypeptide of the invention for treating and/or activating target tissue-specific surface proteins in a subject, e.g., cellular transfection, gene therapy, direct administration with a delivery vehicle or pharmaceutically acceptable carrier, indirect delivery by providing recombinant cells comprising a nucleic acid encoding a targeting fusion polypeptide of the invention.

Various delivery systems are known and can be used to administer the fusion polypeptide of the invention, e.g., encapsulation in liposomes, microparticles, microcapsules, recombinant cells capable of expressing the compound, receptor-mediated endocytosis (see, e.g., Wu and Wu, 1987, J. Biol. Chem. 262:4429-4432), construction of a nucleic acid as part of a retroviral or other vector, etc. Methods of introduction can be enteral or parenteral and include but are not limited to intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, pulmonary, intranasal, intraocular, epidural, and oral routes. The compounds may be administered by any convenient route, for example by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and may be administered together with other biologically active agents. Administration can be systemic or local. In addition, it may be desirable to introduce the pharmaceutical compositions of the invention into the central nervous system by any suitable route, including intraventricular and intrathecal injection; intraventricular injection may be facilitated by an intraventricular catheter, for example, attached to a reservoir, such as an Ommaya reservoir. Pulmonary administration can also be employed, e.g., by use of an inhaler or nebulizer, and formulation with an aerosolizing agent.

In a specific embodiment, it may be desirable to administer the pharmaceutical compositions of the invention locally to the area in need of treatment; this may be achieved, for example, and not by way of limitation, by local infusion during surgery, topical application, e.g., by injection, by means of a catheter, or by means of an implant, the implant being of a porous, non-porous, or gelatinous material, including membranes, such as sialastic membranes, fibers, or commercial skin substitutes.

In another embodiment, the active agent can be delivered in a vesicle, in particular a liposome (see Langer (1990) Science 249:1527-1533). In yet another embodiment, the active agent can be delivered in a controlled release system. In one embodiment, a pump may be used (see Langer (1990) supra). In another embodiment, polymeric materials can be used (see Howard et al. (1989) J. Neurosurg. 71:105). In another embodiment where the active agent of the invention is a nucleic acid encoding a protein, the nucleic acid can be administered in vivo to promote expression of its encoded protein, by constructing it as part of an appropriate nucleic acid expression vector and administering it so that it becomes intracellular, e.g., by use of a retroviral vector (see, for example, U.S. Pat. No. 4,980,286), or by direct injection, or by use of microparticle bombardment (e.g., a gene gun; Biolistic, Dupont), or coating with lipids or cell-surface receptors or transfecting agents, or by administering it in linkage to a homeobox-like peptide which is known to enter the nucleus (see e.g., Joliot et al., 1991, Proc. Natl. Acad. Sci. USA 88:1864-1868), etc. Alternatively, a nucleic acid can be introduced intracellularly and incorporated within host cell DNA for expression, by homologous recombination.

Cellular Transfection and Gene Therapy

The present invention encompasses the use of nucleic acids encoding the fusion polypeptides of the invention for transfection of cells in vitro and in vivo. These nucleic acids can be inserted into any of a number of well-known vectors for transfection of target cells and organisms. The nucleic acids are transfected into cells ex vivo and in vivo, through the interaction of the vector and the target cell. The compositions are administered (e.g., by injection into a muscle) to a subject in an amount sufficient to elicit a therapeutic response.

In another aspect, the invention provides a method of treating a target site, i.e., a target cell or tissue, in a human or other animal comprising transfecting a cell with a nucleic acid encoding a tissue-specific fusion polypeptide of the invention, wherein the nucleic acid comprises an inducible promoter operably linked to the nucleic acid encoding the targeting fusion polypeptide. For gene therapy procedures in the treatment or prevention of human disease, see for example, Van Brunt (1998) Biotechnology 6:1149-1154.

Combination Therapies

In numerous embodiments, the fusion polypeptides of the present invention may be administered in combination with one or more additional compounds or therapies. For example, multiple fusion polypeptides can be co-administered in conjunction with one or more therapeutic compounds. The combination therapy may encompass simultaneous or alternating administration. In addition, the combination may encompass acute or chronic administration.

Pharmaceutical Compositions

The present invention also provides pharmaceutical compositions comprising a fusion protein of the invention and a pharmaceutically acceptable carrier. The term “pharmaceutically acceptable” means approved by a regulatory agency of the Federal or a state government or listed in the U.S. Pharmacopeia or other generally recognized pharmacopeia for use in animals, and more particularly in humans. The term “carrier” refers to a diluent, adjuvant, excipient, or vehicle with which the therapeutic is administered. Such pharmaceutical carriers can be sterile liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil and the like. Suitable pharmaceutical excipients include starch, glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, ethanol and the like. The composition, if desired, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. These compositions can take the form of solutions, suspensions, emulsion, tablets, pills, capsules, powders, sustained-release formulations and the like. The composition can be formulated as a suppository, with traditional binders and carriers such as triglycerides. Oral formulation can include standard carriers such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc. Examples of suitable pharmaceutical carriers are described in “Remington's Pharmaceutical Sciences” by E. W. Martin.

In a preferred embodiment, the composition is formulated in accordance with routine procedures as a pharmaceutical composition adapted for intravenous administration to human beings. Where necessary, the composition may also include a solubilizing agent and a local anesthetic such as lidocaine to ease pain at the site of the injection. Where the composition is to be administered by infusion, it can be dispensed with an infusion bottle containing sterile pharmaceutical grade water or saline. Where the composition is administered by injection, an ampoule of sterile water for injection or saline can be provided so that the ingredients may be mixed prior to administration.

The active agents of the invention can be formulated as neutral or salt forms. Pharmaceutically acceptable salts include those formed with free amino groups such as those derived from hydrochloric, phosphoric, acetic, oxalic, tartaric acids, etc., and those formed with free carboxyl groups such as those derived from sodium, potassium, ammonium, calcium, ferric hydroxides, isopropylamine, triethylamine, 2-ethylamino ethanol, histidine, procaine, etc.

The amount of the tissue-specific fusion polypeptide of the invention which will be effective in the treatment of a tissue-related condition or disease can be determined by standard clinical techniques based on the present description. In addition, in vitro assays may optionally be employed to help identify optimal dosage ranges. The precise dose to be employed in the formulation will also depend on the route of administration, and the seriousness of the condition, and should be decided according to the judgment of the practitioner and each subject's circumstances. However, suitable dosage ranges for intravenous administration are generally about 20-5000 micrograms of active compound per kilogram body weight. Suitable dosage ranges for intranasal administration are generally about 0.01 pg/kg body weight to 1 mg/kg body weight. Effective doses may be extrapolated from dose-response curves derived from in vitro or animal model test systems.

Kits

The invention also provides a pharmaceutical pack or kit comprising one or more containers filled with at least one targeting fusion polypeptide or nucleic acid encoding a fusion polypeptide of the invention. The kits of the invention may be used in any applicable method, including, for example, diagnostically. Optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects (a) approval by the agency of manufacture, use or sale for human administration, (b) directions for use, or both.

Transgenic Animals

The invention includes transgenic non-human animals expressing a fusion polypeptide of the invention. A transgenic animal can be produced by introducing nucleic acid into the male pronuclei of a fertilized oocyte, e.g., by microinjection, retroviral infection, and allowing the oocyte to develop in a pseudopregnant female foster animal. Any of the regulatory or other sequences useful in expression vectors can form part of the transgenic sequence. A tissue-specific regulatory sequence(s) can be operably linked to the transgene to direct expression of the transgene to particular cells. A transgenic non-human animal expressing a tissue-specific fusion polypeptide of the invention is useful in a variety of applications, including as a means of producing such fusion proteins. Further, the transgene may be placed under the control of an inducible promoter such that expression of the tissue-specific fusion polypeptide may be controlled by, for example, administration of a small molecule.

Specific Embodiments

Example 1 illustrates embodiments of the fusion proteins of the invention targeted to skeletal muscle for the treatment of a deleterious skeletal muscle condition. More specifically described are muscle-specific fusion proteins comprising agrin and human insulin like growth factor 1 (hIGF-1) and variants thereof, as well as fusion polypeptides comprising agrin, hIGF1 and hIGF1 variants and human growth hormone (hGH) and fusion polypeptides comprising hIGF1 and variants thereof and hGH. Example 2 describes inventions which demonstrate the use of cadherins to produce the targeted fusion polypeptides of the invention. Example 3 described embodiments that demonstrate the use of follistatin and related molecules as the active or therapeutic agents in the fusion polypeptides of the invention. Example 4 describes embodiments of the fusion proteins of the invention that are active on endothelial cells. Example 5 describes myostatin-inhibiting fusion polypeptides of the invention.

EXAMPLES

The following example is put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the methods and compositions of the invention, and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.

Example 1 Muscle Targeting Fusion Polypeptides

Exemplification of the fusion polypeptides of the invention include: human IGF-1 (r3long)-linker-50 Kd COOH terminal of human agrin 0,8 (SEQ ID NO:1); Processed form of human IGF-1 (r3long)-linker-50 Kd COOH terminal of human agrin 0,8 (without signal sequence) (SEQ ID NO:2); hIGF-1-linker-50 Kd COOH terminal of human agrin 0,8 (without signal sequence) (SEQ ID NO:3); processed form of hIGF-1-linker-50 Kd COOH terminal of human agrin 0,8 (without signal sequence) (SEQ ID NO:4); hIGF1(r3long)-linker-50 Kd COOH terminal of human agrin 0,8 (SEQ ID NO: 5); processed form of hIGF-1 (r3long)-linker-50 Kd COOH terminal of human agrin 0,8 (without signal sequence) (SEQ ID NO:6); hIGF1-linker-50 Kd COOH terminal of human agrin 0,0 (without signal sequence) (SEQ ID NO:7); processed form of hIGF-1-linker-50 Kd COOH terminal of human agrin 0,0 (without signal sequence) (SEQ ID NO:8); mature human IGF1(deI GPE, deIR37)-Fc (SEQ ID NO:9); mature human IGF1(deI GPE, deIR37) (SEQ ID NO:10); mature human IGF1(deI GPE, deIR37) with GTG linker (SEQ ID NO:11); hGH-hIGF1-hAgrin 0,8 (SEQ ID NO:12); hGH-hIGF1 -hFc (SEQ ID NO:13); hGH-hIGF1 with GTG linker (SEQ ID NO:14); hGH-hIGF2-hAgrin 0,8 (SEQ ID NO:15); hGH-hIGF2-hFc (SEQ ID NO:16); hGH-hIGF2 (SEQ ID NO:17); hGH-IGF1 (SEQ ID NO:18); hGH-hIGF1 (A37) (SEQ ID NO:19); hGH-hIGF1 (delete R37) (SEQ ID NO:20); hGHe-hIGF1 (mutated R3, A37) (SEQ ID NO:21); hGH-hIGF1 (mutated R3delete R 37) (SEQ ID NO:22); hGH-hIGF1(delete R37) (SEQ ID NO:23); hGH-hIGF1 (Del GPE) (SEQ ID NO:24); hGH-hIGF1 (Del GPE, del R37) (SEQ ID NO:25); hGH-hIGF1-human agrin 0,8 (SEQ ID NO:26); hGH-hIGF1(deI GPE)-human agrin 0,8 (SEQ ID NO:27); hGH-hIGF1 (del R37)-human agrin 0,8 (SEQ ID NO:28); hGH-hIGF1(A37)-human agrin 0,8 (SEQ ID NO:29); hGH-hFc-hIGF1 (SEQ ID NO:30); hGH-hFc-hIGF1(del R37) (SEQ ID NO:31); hGH-hFc-hIGF1 (deI GPE) (SEQ ID NO:32); hGH-hFc-hIGF1 (deI GPE, del R37) (SEQ ID NO:33). Further embodiments include the Tercera mutant form of IGF-1 linked to human agrin (0,8 or 0,0), and mutant forms of human IGF1 or IGF2 (such as set forth in SEQ ID NOS:10 or 11) used alone, linked to a multimerizing component (such as Fc; SEQ ID NO:9) or linked to human agrin.

The fusion protein constructs or molecules (1) human growth hormone-human IGF1; (2) human growth hormone-human IGF1-human Fc; (3) human growth hormone-human IGF1-human agrin 0,8; (4) human IGF1-Fc (Δ3, deIR37); (5) human growth hormone and (6) human IGF1-agrin, were compared on C2C12 myotubes for their ability to activate various receptors and signaling pathways. The activity of IGF-1 was measured by its ability to phosphorylate the IGF-1 receptor and Akt kinase. The activity of human growth hormone (hGH) was measured by its ability to phosphorylate Stat5. The activity of agrin was measured by its ability to phosphorylate the MuSK receptor. Glass et al. (1996) 85:513-523; Beguinot et al. (1988) Biochemistry. 27(9):3222-8.

Phosphorylation assays indicated that fusion proteins having the configuration hGH-IGF1 which includes both hGH and hIGF1 is capable of simultaneously activating the IGF1 Receptor, Akt, and Stat5. Such phosphorylation was determined by a Western blot, using phospho-specific antibodies to the various molecules, or by immune-precipitating the receptors (such as IGFR), and Westerning with an antibody specific to anti-phospho-tyrosine. In addition, all of the above fusion polypeptides were made using human IGF1 mutants which had the first three amino acids deleted (Δ3) and either elimination or substitution of the arginines at positions 36 and/or 37. Such mutant IGF1 molecules demonstrated both resistance to cleavage as well as reduced binding by IGF-1 binding proteins (specifically IGF1 binding protein 5) without affecting signaling ability on C2C12 myotubes.

A fusion protein which includes hGH and hIGF1 and agrin simultaneously activates the IGF1 Receptor, Akt, Stat5, and the MuSK receptor, as determined by a Western blot, using phospho-specific antibodies to the various molecules, or by immune-precipitating the receptors (such as IGFR or MuSK), and Westerning with an antibody specific to anti-phospho-tyrosine. A fusion protein which includes IGF1 and agrin 0,8 activates the IGF1 receptor and binds and activates the MuSK receptor, thus providing muscle specificity. Constructs using agrin 0,0 were able to bind but not activate the MuSK receptor, thus demonstrating the use of this form of agrin for targeting muscle cells or tissue. Contacting C2C12 myotubes with the IGF1-GH fusion caused greater hypertrophy than IGF1 alone or GH alone.

Proliferin may be substituted for hGH in any of the above constructs (Wilder, E. L. et al. (1989) Mol. Cell Biol. 9(2):430-441. Assessment of proliferin activity may include assays for neoangiogenesis (Jackson et al. Science (1994) 266:1581-1584. The human proliferin sequence is shown in SEQ ID NO: 34.

Example 2 Muscle Targeting Fusion Polypeptides Using Cadherins

M-Cadherin containing fusion polypeptides for targeting muscle tissue were prepared using the following amino acid sequences: IGF1-muscle cadherin (SEQ ID NO:35) (containing 4 M-Cadherin domains)-IGF1; mature IGF1 (SEQ ID NO:36); full-length muscle cadherin (Cadherin 15) (SEQ ID NO:37); muscle cadherin extracellular domain containing 4 cadherin domains (SEQ ID NO:38); 4 muscle cadherin domains fused to SEAP (SEQ ID NO:39); 3 muscle cadherin domains (SEQ ID NO:40); 3 muscle cadherin domains fused to SEAP (SEQ ID NO:41); 2 muscle cadherin domains fused to SEAP (SEQ ID NO:42).

A fusion protein containing 4 N-terminal cadherin domains (SEQ ID NO:36) of human muscle cadherin (Cadherin 15) binds to skeletal muscle satellite cells. Secreted alkaline phosphatase (SeAP) was fused to the COOH terminus of a component containing 2 (SEQ ID NO:42), 3 (SEQ ID NO:41) or 4 (SEQ ID NO:39) cadherin domains of M-cadherin. Using antibodies to SEAP, it was determined that the fusion proteins containing either 3 or 4 N-terminal cadherin domains, but not the fusion protein containing 2 cadherin domains, bound C2C12 myoblast cells, but not fibroblasts, thus demonstrating their specificity for muscle cells.

In another embodiment, insulin-like growth factor 1 or a variant thereof (SEQ ID NOS:10 and 36) was fused to either four cadherin domains (SEQ ID NO:38) or 3 cadherin domains (SEQ ID NO:40) of M-cadherin to create muscle-specific polypeptides. In this case, C2C12 myotubes contacted with the fusion proteins hypertrophied, indicating that the IGF1 was active and that it bound to the C2C12 muscle cells. In an alternative embodiment, two IGF-1 molecules were fused to a polypeptide comprising 4 cadherin domains to create a muscle-specific fusion polypeptide (SEQ ID NO:35), which can also cause muscle hypertrophy.

Example 3 Muscle-Targeting Fusion Polypeptides Using Follistatin and Related Molecules

The following protein sequences were also used to prepare muscle-specific fusion polypeptides that comprise the myostatin-inhibiting proteins follistatin (SEQ ID NO:43), FSTL1 (SEQ ID NO:44), and FLRG (also known as FSL3) (SEQ ID NO:45).

Follistatin, FSTLI and FLRG sequences (SEQ ID NOS: 43, 44 and 45) are fused to three or 4 N-terminal domains (SEQ ID NO: 40 or 38) of M-cadherin. These fusion proteins all block myostatin-mediated phosphorylation of SMAD2, indicating that they are functional. Such fusion proteins can be used to block myostatin-mediated atrophy, or myostatin-mediated inhibition of differentiation, with the advantage of being muscle-specific.

Example 4 Vascular Endothelial Cell-Targeting Fusion Polypeptides

Fusion polypeptides comprising vascular endothelial (VE)-cadherin extracellular domains useful for targeting vascular tissue were prepared using the following amino acid sequences, as well as the human sequence set forth in Ludwig et al. (2000) supra. VE-cadherin Domain One (SEQ ID NO:46); VE-cadherin Domain Two (SEQ ID NO:47); VE-cadherin Domain Three (SEQ ID NO:48); VE-cadherin Domain Four (SEQ ID NO:49); and VE-cadherin Domain Five (SEQ ID NO:50).

Fusion proteins that comprise cadherin domains 1-5 (SEQ ID NOS 46-50), 14 (SEQ ID NOS:46-49), and 1-3 (SEQ ID NOS:46-48) of human VE cadherin (Cadherin 5), bind to vascular endothelial cells. When secreted alkaline phosphatase (SEAP) is fused to the COOH terminus of a component comprising four N-terminal domains of VE-cadherin (SEQ ID NOS:46-49), the protein binds endothelial cells but not fibroblasts.

In another embodiment of this example, vascular endothelial growth factor (VEGF) is fused to amino acids 18-583 of VE-Cadherin as described in Ludwig, D. et al. (2000) supra, which comprises SEQ ID NOS:46-49. In this case, endothelial cells demonstrate phosphorylation of the VEGF receptor, and activation of Akt, indicating that the VEGF receptor is bound and activated.

Example 5 Myostatin Inhibiting Fusion Polypeptide Constructs

The following fusion polypeptides were constructed to demonstrate the use of human myostatin propeptide in constructs which block myostatin activity: optional 23 amino acid signal sequence, human myostatin propeptide-human Fc1 (SEQ ID NO: 51); optional 23 amino acid signal sequence, the active component is human myostatin propeptide, and the targeting component is human agrin (SEQ ID NO:520; optional SS of 23 amino acids, active agent is human myostatin propeptide, and targeting component is fragment of human agrin (SEQ ID NO:53); optional SS of 23 amino acids, active agent is human myostatin propeptide, and multimerizing component is human Fc protein (SEQ ID NO:54).

C2C12 myoblasts are grown to confluence and differentiated into myotubes. Differentiation is accomplished by switching to differentiation media—2% Horse Serum, in DMEM. Forty eight (48) to ninety six (96) hours post-differentiation the myotubes are starved for four (4) hours, in serum-free media. For this experiment, plates of myotubes are treated in groups of two, for fifteen minutes, as follows: (a) untreated, (b) 100 ng/ml active myostatin, (c) a myostatin inhibitor of the instant invention (for example, the pre-pro domain of myostatin fused to an Fc, or the pre-pro domain of myostatin fused to agrin), at concentrations which could range from 10 ng/ml to 10 ug/ml (d) active myostatin plus a myostatin inhibitor of the instant invention. After treatment, the myotubes are lysed, for example, in NP40 lysis buffer containing phosphatase and protease inhibitors. The resulting lysates are then processed for Western blot analysis with an antibody specific for phosphorylated Smad2, and, as a control for total protein levels, a second Western was performed using an antibody which recognizes nonphosphorylated Smad2. The assay demonstrates that myostatin (GDF8) induces SMAD 2 phosphorylation and that the myostatin inhibitors described above block myostatin-mediated phosphorylation of Smad2. 

1. A modified human insulin-like growth factor-1 (IGF-1) fusion polypeptide, comprising: a deletion of amino acids 1-3 and a deletion of amino acid 37, relative to mature human IGF-1, and a multimerizing component capable of forming a multimer with another said modified IGF-1 fusion polypeptide, wherein the multimerizing component is an Fc domain from IgG1, IgG2, IgG3, or IgG4.
 2. The fusion polypeptide of claim 1, comprising the amino acid sequence of SEQ ID NO:9.
 3. An isolated nucleic acid molecule encoding the fusion polypeptide of claim
 1. 4. A composition comprising the fusion polypeptide of claim 1 and a pharmaceutically acceptable carrier. 